While managers are allowed to make comments on an official's performance, the FA insists they must not imply bias, question their integrity or engage in what could be construed as a personal attack.

Ferguson's comments suggested that Wiley was not fit enough to keep up with the pace of the action at Old Trafford.

"You see referees abroad who are as fit as a butcher's dog. He was taking 30 seconds to book a player," added Ferguson, who was also critical of Wiley's decision-making.

Ferguson twice headed towards the touchline during the second half to make his feelings known about decisions made by the officials.

At one point, after he felt midfielder Anderson had been denied a penalty, he jabbed his finger at fourth official Mike Dean and then pointed angrily to the pitch.

Arsenal boss Arsene Wenger, who was sent to the stands for kicking a water bottle in frustration during the Gunners defeat at Old Trafford earlier in the season, believes referees should "keep their distance" from both players and managers.

"I have no relationship with the referee. I never speak to any referee," said Wenger.

"I respect the referees and I think they have to keep their distances from the managers and the players."

However, the Frenchman accepts there has to be censure for those who overstep the mark.

"You know we are sometimes too excessive after the games," he added.

"What we want is for everybody to be treated exactly the same so there is only one rule in the Premier League.

"When the managers do not respect the code of conduct, this rule has to be applied to everybody and I don't think even Ferguson would want to be treated differently."

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